A mobile communication system is often configured to communicate data blocks (packet) at predetermined communication intervals, and to also communicate control data for the communication control of the data blocks at the same communication intervals as the data blocks.
One example of such communication system is a mobile communication system adopting E-DCH (enhanced dedicated channel) (See 3GGP TR25.896 v2.0.0 “Feasibility Study for Enhanced Uplink for UTRA FDD” (2004-03)). The E-DCH (enhanced dedicated channel) is one of the most important specifications which have been considered to be applied to the WCDMA (Wideband Code Division Multiple Access) system. In the E-DCH, the HARQ (hybrid Automatic Repeat Request) have been considered to be adopted, and a mobile communication system that adopts the HARQ in the E-DCH is configured to communicate data blocks and ACK/NACK (acknowledgement/negative acknowledgement) messages between base stations and mobile stations at predetermined TTIs (transmission time intervals). The ACK/NACK message is a control data by which a receiving side which receives a data block informs the sending side which has transmitted the data block of whether the receiving side has successfully received the data block. For the case when a mobile station sends a data block to a base station, for example, the base station informs the mobile station of whether the base station successfully have received the data block by transmitting an ACK/NACK message through a downlink. When the sending side is informed by the ACK/NACK message that a certain data block is not successfully received, the sending side retransmits the data block.
Additionally, a mobile communication system that adopts the E-DCH is configured so that an RR (rate request) message and an RG (rate grant) message can be communicate between a base station and a mobile station. The RR message is a control data by which a mobile station requests a base station to update the maximum value of the transmission rate of the uplink. As is well known to those skilled in the art, a mobile station is provided with a TFCS (transport format combination set) composed of multiple TFCs (transport format combinations) in the mobile communication system that adopts the E-DCH. A base station determines allowed TFCs (allowed transport format combinations) out of the TFCS, and informs the mobile station of the set of the allowed TFCs. The mobile station selects one TFC from the allowed TFCs, and performs communication through the uplink using the selected TFC. The determination of the allowed TFCs is equivalent to determination of the maximum value of the transmission rate, because respective TFCs correspond to different transmission rates. The RR message is a control data by which the mobile station requests the base station to update the allowed uplink transport format combination subset. The mobile station generates an RR message from the status of the allowed transmitting power, and the desired transmission rate of the service. The transmission of the RR message is equivalent to the fact that the mobile station requests the base station to update the maximum value of the transmission rate of the uplink. The RG message, on the other hand, is a control data by which a base station updates the maximum value of the transmission rate of the uplink, more specifically, control data used for updating the allowed TFCs. It should be noted that the update of the allowed TFCs is equivalent to the update of the maximum value of the transmission rate of the uplink. The update of the allowed TFCs is achieved as follows: A mobile station is provided with an UE pointer that specifies allowed TFCs. The UE pointer indicates a TFC corresponding to the maximum transmission rate out of the allowed TFCs (hereinafter, referred to as the maximum TFC). The RG message includes an instruction increasing or decreasing the UE pointer, or a value indicative of the maximum TFC itself. The mobile station updates the UE pointer in response to the RG message, and thereby updates the allowed TFCs.
One issue of such mobile communication system is the suppression of the occurrence of the communication delay resulting from a communication error of control data. For example, occurrence of communication error of an ACK/NACK message may result in communication delay of data blocks. Let us assume a case when, although a base station actually transmits an ACK/NACK message indicating “NACK” to a mobile station after unsuccessful reception of a data packet, the mobile station erroneously recognizes that the ACK/NACK message indicates “ACK”. In this case, the physical layer within the mobile station discards the data packet transmitted to the base station from the buffer, and starts to transmit the next data packet. Therefore, retransmission of the data packet that has not successfully received to the base station requires retransmission of the data packet from the upper layer to the physical layer. This causes large delay in the communication of data packets. When the retransmission from the upper layer to the physical layer can not be achieved, it results in loss of the data packet.
The same issue may apply to the RG messages and the RR messages. The base station of a WCDMA system is configured to reduce the noise rise thereof through transmitting an RG message to a mobile station to request the decrease in the maximum TFC, when the noise rise reaches near the quality threshold. Here, a noise rise of a certain base station is the ratio of the total received power to the noise power at the base station. However, the mobile station may transmit the next data block using a TFC corresponding to further higher transmission rate, when the mobile station erroneously receives the RG message and erroneously recognized that the mobile station is requested to increase the maximum TFC. This may further increase the noise rise of the base station, and result in deterioration of the reception quality of the uplink. Similarly, the base station may assign inappropriate allowed TFTs to the mobile station, when unsuccessfully receiving an RR message. For example, the base station may allow the mobile station to use a TFC corresponding to an unnecessarily high transmission rate, due to the erroneous reception of an RR message. This may prevent a mobile station which actually requires a TFC corresponding to a high transmission rate from using the TFC corresponding to the high transmission rate. Additionally, a base station may erroneously decide that a mobile station requests the decrease in the maximum TFC although the maximum TFC can be increased from the viewpoint of the noise rise, because of the unsuccessful reception of the RR message. This results in that an inappropriate decrease in the maximum TFC of the mobile station. As thus described, unsuccessful reception of RG and RR messages hinders the effective use of the resource, and causes the decrease in the throughput and the deterioration of the reception quality.
A technique is commonly known in which the same data is repeatedly transmitted to improve the communication reliability, and this technique is applicable to the communication of the control data in the above-described system. However, repeated transmission of the same control data over multiple TTIs results in an undesirable result as follows: Firstly, repeated transmission of an ACK/NACK message associated with one data block undesirably reduces the throughput of communication of data blocks. As shown in FIG. 1B, only one data block can transmitted for every two TTIs, when an ACK/NACK message associated with a data block is transmitted twice. Compared with the case that an ACK/NACK message associated with a data block is transmitted only once (See FIG. 1A), transmitting an ACK/NACK message associated with a data block twice results in undesired decrease in the throughput. Secondly, repeated transmission of the same control data over multiple TTIs undesirably reduces the transmission rate of the control data per one TTI, and undesirably increases the control cycle period. When the same control data is transmitted twice over two TTIs, the minimum update cycle period of the control data is 2 TTIs. This undesirably decreases the response of the communication control.
Various other approaches have been proposed for improving the reliability and throughput of the communication of the control data. Japanese Laid Open Patent Application No. JP-A 2001-308711 discloses a communication method of control information data in a communication system adopting 8B/10B coding. The disclosed communication method is directed to enable error detection of the communicated control information codes. On the sending side, a 22-bit-length control information data is divided into two 8-bit-length blocks and a single 6-bit-length block. The 8-bit length blocks are coded into 10-bit-length control information code through 8B/10B coding. Additionally, a 2-bit-length parity control corresponding to the 22-bit-length control information data is generated, and another 8-bit-length block is generated through attaching the 2-bit-length parity control to the 6-bit-length block. The 8-bit-length block generated is coded into a 10-bit-length control information code.
Japanese Laid-Open Patent Application No. JP-A Heisei 6-197150 discloses a technique for reducing communications traffic used for the control in which control information for the flow control is not exchanged if unnecessary. In this technique, transmission intervals at which the sending side transmits data are controlled in response to time intervals at which reception data are stored in a reception buffer on the receiving side, and time intervals at which the reception data are outputted from the reception buffer. The communications traffic for the control is reduced through appropriate control of the transmission intervals.
Japanese Laid-Open Patent Application No. JP-A 2003-179581 discloses a technique in which ACK/NACK messages are flexibly transmitted without signal transmission overhead through transmitting the ACK/NACK messages at time intervals different from time intervals at which data packets are transmitted.
Japanese Laid-Open Patent Application No. 2000-78118 discloses a technique for reducing erroneous operations resulting from erroneous reception of ARQ control data. In this technique, a plurality of blocks within a transmission frame is attached with one ARQ control data containing an error correction code, and a plurality of blocks of ACK/NACK messages within a response frame is attached with one ARQ control data. In the time domain, a super frame consisting of the transmission frame and the response frame is defined to optimize the communication timing.
Japanese Laid-Open Patent Application No. JP-A Heisei 7-38540 discloses a technique for reducing the ratio of ARQ control data to transmission data, and improving the throughput. In this technique, the sending side divides transmission data into a plurality of blocks attached with an error detection code, and transmits transmission data which are attached with one ARQ control data for N blocks. The reception side performs error detection on the respective blocks. When detecting an error, the receiving side issues a retransmission request. The sending side generates error correction codes for blocks relevant to the retransmission request, and generates a retransmission frame attached with one ARQ control data through incorporating the error correction codes. The reception side reproduces the correct data from the error correction codes within the re-transmission frame and the erroneous blocks which have been received.
Japanese Laid-Open Patent Application No. JP-A Heisei 7-123079 discloses a technique for maintaining the throughput by using a simple protocol. In this technique, the sending side successively transmits M blocks, and the receiving side successively performs error detection on these M blocks. When an error is detected in the i-th block, the reception side discards the i-th to M-th blocks, and returns a retransmission request response NAK for the i-th block. In response to the retransmission request response NAK, the sending side successively transmits i-th to (M+i−1)-th blocks. The receiving side successively performs error detection on these M blocks. Such process is repeated till all of the desired blocks are successfully received.
In accordance with the inventor's study, however, there is room for further improvement in these prior art.